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| gettext | |
|---|---|
| Original author | Sun Microsystems[1] |
| Developer | various |
| Initial release | 1990; 36 years ago (1990)[2] |
| Stable release | |
| Operating system | Cross-platform |
| Type | Internationalization and localization |
| License | Variousfree software licenses |
| Website | www |
| Repository | various based on OpenSolaris and GNU gettext |
Incomputing,gettext is aninternationalization and localization (i18n and l10n) system commonly used for writing multilingual programs onUnix-like computeroperating systems. One of the main benefits of gettext is that it separates programming from translating.[4] The most commonly used implementation of gettext isGNU gettext,[5] released by theGNU Project in 1995. The runtime library islibintl. gettext provides an option to use different strings for any number ofplural forms of nouns, but this feature has no support forgrammatical gender. The mainfilename extensions used by this system are.POT (Portable Object Template),.PO (Portable Object) and .MO (Machine Object).[6]
Initially, POSIX provided no means of localizing messages. Two proposals were raised in the late 1980s, the 1988 Uniforum gettext and the 1989 X/Open catgets (XPG-3 § 5).Sun Microsystems implemented the first gettext in 1993.[1] The Unix and POSIX developers never really agreed on what kind of interface to use (the other option is the X/Open catgets), so manyC libraries, includingglibc, implemented both.[7] As of August 2019[update], whether gettext should be part of POSIX was still a point of debate in theAustin Group, despite the fact that its old foe has already fallen out of use. Concerns cited included its dependence on the system-set locale (aglobal variable subject to multithreading problems) and its support for newer C-language extensions involving wide strings.[8]
TheGNU Project decided that the message-as-key approach of gettext is simpler and more friendly. (Most other systems, including catgets, requires the developer to come up with "key" names for every string.)[9] They released GNU gettext, afree software implementation of the system in 1995.[2] Gettext, GNU or not, has since been ported to many programming languages.[10] The simplicity of po and widespread editor support even led to its adoption in non-program contexts for text documents or as an intermediate between other localization formats, with converters like po4a (po for anything) and Translate Toolkit emerging to provide such a bridge.[11][12]
The basic interface of gettext is thegettext(const char*) function, which accepts astring that the user will see in the original language, usually English. To save typing time and reduce code clutter, this function is commonlyaliased to_:[13]
printf(gettext("My name is %s.\n"),my_name);printf(_("My name is %s.\n"),my_name);// same, but shorter
gettext() then uses the supplied strings as keys for looking up translations, and will return the original string when no translation is available. This is in contrast toPOSIXcatgets(),[14]AmigaOSGetString(),[15] orMicrosoft WindowsLoadString() where a programmatic ID (often an integer) is used. To handle the case where the same original-language text can have different meanings, gettext has functions likecgettext() that accept an additional "context" string.
xgettext is run on the sources to produce a.pot (Portable Object Template) file, which contains a list of all the translatable strings extracted from the sources. Comments starting with/// are used to give translators hints, although other prefixes are also configurable to further limit the scope. One such common prefix isTRANSLATORS:.
For example, an input file with a comment might look like:
/// TRANSLATORS: %s contains the user's name as specified in Preferencesprintf(_("My name is %s.\n"),my_name);
xgettext is run using the command:
xgettext -c /
The resultant .pot file looks like this with the comment (note that xgettext recognizes the string as aC-languageprintf format string):
#. TRANSLATORS: %s contains the user's name as specified in Preferences#, c-format#: src/name.c:36msgid"My name is %s.\n"msgstr""
In POSIXshell script, gettext provides agettext.sh library one can include that provides the many same functions gettext provides in similar languages.[16]GNU bash also has a simplified construct$"msgid" for the simple gettext function, although it depends on the C library to provide agettext() function.[17]
The translator derives a.po (Portable Object) file from the template using themsginit program, then fills out the translations.[18]msginit initializes the translations so, for instance, for a French language translation, the command to run would be:[6]
msginit --locale=fr --input=name.pot
This will createfr.po. The translator then edits the resultant file, either by hand or with a translation tool likePoedit, orEmacs with its editing mode for.po files. An edited entry will look like:
#: src/name.c:36msgid"My name is %s.\n"msgstr"Je m'appelle %s.\n"
Finally, the .po files are compiled withmsgfmt into binary.mo (Machine Object) files. GNU gettext may use its own file name extension.gmo on systems with another gettext implementation.[19] These are now ready for distribution with the software package.
GNUmsgfmt can also perform some checks relevant to theformat string used by the programming language. It also allows for outputting to language-specific formats other than MO;[20] theX/Open equivalent isgencat.
In later phases of the developmental workflow,msgmerge can be used to "update" an old translation to a newer template. There is alsomsgunfmt for reverse-compiling.mo files, and many other utilities for batch processing.
The user, onUnix-type systems, sets theenvironment variableLC_MESSAGES, and the program will display strings in the selected language, if there is an.mo file for it.
Users onGNU variants can also use the environment variableLANGUAGE instead. Its main difference from the Unix variable is that it supports multiple languages, separated with a colon, for fallback.[21]
Thengettext() interface accounts for the count of a noun in the string. As with the convention ofgettext(), it is often aliased toN_ in practical use. Consider the code sample:
// parameters: english singular, english plural, integer countprintf(ngettext("%d translated message","%d translated messages",n),n);
A header in the"" (empty string) entry of the PO file stores some metadata, one of which is the plural form that the language uses, usually specified using a C-styleternary operator. Suppose we want to translate for theSlovene language:
msgid""msgstr"""...""Language: sl\n""Plural-Forms: nplurals=4; plural=(n%100==1 ? 1 : n%100==2 ? 2 : n%100==3 || n%100==4 ? 3 : 0);\n"
Since now there are four plural forms, the final po would look like:
#: src/msgfmt.c:876#, c-formatmsgid"%d translated message"msgid_plural"%d translated messages"msgstr[0]"%d prevedenih sporočil"msgstr[1]"%d prevedeno sporočilo"msgstr[2]"%d prevedeni sporočili"msgstr[3]"%d prevedena sporočila"
Reference plural rules for languages are provided by theUnicode consortium.[22] msginit also prefills the appropriate rule when creating a file for one specific language.[18]
In addition toC, gettext has the following implementations:C# for bothASP.NET[23][24] and forWPF,[25]Perl,[26]PHP,[27]Python,[28]R,[29]Scala,[30] andNode.js.[31]
GNU gettext has native support for Objective-C, but there is no support for theSwift programming language yet. A commonly used gettext implementation on these Cocoa platforms is POLocalizedString.[32] The Microsoft Outlook for iOS team also provides a LocalizedStringsKit library with a gettext-like API.[33]
